Method for manufacturing a semiconductor device

ABSTRACT

A semiconductor device is manufactured by the use of a glass substrate which has previously been heated. An amorphous semiconductor layer is formed on the previously heated glass substrate and then crystallized by heat. By virtue of the previous heating, shrink of the glass substrate after the crystallization process is reduced. Accordingly, internal stress is not generated in the crystallized semiconductor layer. The semiconductor device thus manufactured is superior in electrical property.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing asemiconductor device.

2. Description of the Prior Art

A technique of forming a non-single crystal semiconductor layer on aglass substrate by reduced pressure CVD or plasma CVD followed byheating the substrate at about 600° C. to thereby crystallize the layerinto a polycrystal semiconductor layer has been well-known in the fieldof manufacture of semiconductor devices. Explaining the process of thisthermal crystallization, first the temperature is raised from roomtemperature (i.e. initial stage), second the temperature is maintainedat about 600° C. (i.e. intermediate stage) for a few hours to severaltens hours, and finally the temperature is lowered to room temperature(i.e. last stage). If a cheap glass substrate utilized for a large-sizedliquid crystal display device and so on is subjected to the thermalcrystallization process at about 600° C., since a cheap glass substratehas its strain point at about 600° C., the glass substrate shrinks (thatis, the volume of the glass at the last stage becomes smaller than thatat the initial stage) and thereby internal stress is caused in asemiconductor layer provided on the substrate. Further, photolithographypattern to be used in the subsequent process is deformed due to theshrink of the glass substrate, so that mask alignment in the furthersubsequent process becomes difficult to carry out. According to anexperiment, interface state in the semiconductor layer formed on thesubstrate was high due to the internal stress, therefore electricalproperty of the semiconductor layer was bad. For the above reason, atechnique for obtaining on a glass substrate a semiconductor layer ofexcellent electrical property has been required in the field ofmanufacture of semiconductor devices.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method formanufacturing a semiconductor device of high performance.

It is another object of the present invention to provide a semiconductordevice comprising a channel region of high field effect mobility.

It is a further object of the present invention to provide asemiconductor device of high performance.

In order to attain these and other objects, first a glass substrate isheated in a non-oxidizing atmosphere or an inactive gas atmosphere at atemperature not higher than strain point of the glass substrate, andthen a non-single crystal semiconductor layer is formed on the substrateand the non-single crystal semiconductor layer is crystallized by heatin a non-oxidizing atmosphere or an inactive gas atmosphere. The volumeof the glass substrate at a temperature, e.g., room temperature afterthe glass substrate heating process is smaller than that at the sametemperature as the above, e.g., room temperature before the glasssubstrate heating process. That is, the glass substrate shrinks afterbeing heated. By virtue of this glass substrate heating process, whenthe non-single crystal semiconductor layer formed on the glass substrateis crystallized by heat, the volume of the glass substrate is notdecreased so much, that is, the shrink of the glass substrate is verylittle. Therefore, a crystallized semiconductor layer free from internalstress can be obtained by the crystallization process.

A non-single crystal semiconductor includes an amorphous semiconductor,a semi-amorphous semiconductor, a microcrystal semiconductor, and animperfect polycrystal semiconductor. The microcrystal semiconductor isdefined as a semiconductor in amorphous state in which crystal state isdispersed. On the other hand, the imperfect polycrystal semiconductor isdefined as a semiconductor in polycrystal state in which crystal growthis imperfect, that is, crystals can be grown more.

Strain point of glass is defined as the temperature at which theviscosity of glass v is 4×10¹⁴ poise (log(v)=14.5).

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to theaccompanying drawings wherein:

FIG. 1 is a graphical view showing the relationship between shrinkingpercentage of a glass substrate and temperature;

FIG. 2 is a graphical view showing the relationship between shrinkingpercentage of a glass substrate and period of heating;

FIG. 3 is a graphical view showing relative intensity in laser Ramanspectroscopic analysis for semiconductor layers;

FIGS. 4(A) through (E) are schematic cross sectional views showing amethod for manufacturing a thin film transistor in accordance with thepresent invention;

FIG. 5 is a graphical view showing drain current-gate voltagecharacteristic of a thin film transistor;

FIG. 6 is a graphical view showing the relationship between gate voltageand field effect mobility in a thin film transistor;

FIG. 7 is a graphical view showing field effect mobility of a thin filmtransistor;

FIG. 8 is another graphical view showing the relationship betweenshrinking percentage of a glass substrate and temperature;

FIG. 9 is another graphical view showing the relationship betweenshrinking percentage of a glass substrate and period of heating;

FIG. 10 is another graphical view showing relative intensity in laserRaman spectroscopic analysis for semiconductor layers;

FIG. 11 is still another graphical view showing relative intensity inlaser Raman spectroscopic analysis for semiconductor layers;

FIGS. 12(A) through (E) are schematic cross sectional views showing amethod for manufacturing a thin film transistor in accordance with thepresent invention;

FIG. 13 is another graphical view showing drain current-gate voltagecharacteristic in a thin film transistor;

FIG. 14 is another graphical view showing the relationship between gatevoltage and field effect mobility in a thin film transistor;

FIG. 15 is still another graphical view showing drain current-gatevoltage characteristic in a thin film transistor;

FIGS. 16(A) through (E) are schematic cross sectional views showing amethod for manufacturing a thin film transistor in accordance with thepresent invention;

FIG. 17 is a further graphical view showing drain current-gate voltagecharacteristic in a thin film transistor;

FIG. 18 is still another graphical view showing the relationship betweengate voltage and field effect mobility in a thin film transistor;

FIG. 19 is another graphical view showing field effect mobility of athin film transistor; and

FIG. 20 is a still further graphical view showing drain current-gatevoltage characteristic in a thin film transistor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Formation of a semiconductor layer on a substrate in accordance with afirst embodiment of the present invention will be described hereinafter.The substrate used in the first embodiment was "AN-2" non-alkali glassproduced by Asahi Glass Company, whose strain point is 616° C. AN-2non-alkali glass comprises SiO₂ (53%), Al₂ O₃ (11%), B₂ O₃ (12%), RO(24%), and R₂ O (0.1%). The glass substrate was heated at 610° C. for 12hours in an electrical furnace. This glass substrate heating was carriedout in an inactive gas atmosphere, e.g. N₂, under an atmosphericpressure.

After the heating, a silicon compound layer, e.g. SiO₂ layer, was formedto be 200 nm thick by sputtering in order to provide a blocking layerfor preventing alkali ions residing in the glass substrate from enteringa device to be formed on the substrate. Then an amorphous silicon layerwas formed thereon to be 100 nm thick. The amorphous silicon layer wasthen heated at 600° C. for 96 hours in an electrical furnace to therebybe crystallized. The crystallization was carried out in an inactive gasatmosphere, e.g. N₂, under an atmospheric pressure, in order to preventthe amorphous silicon layer from reacting with a gas, e.g. oxygen.

Relationship between shrinking percentages and temperatures is examinedas follows.

Glass substrates A ("AN-2" non-alkali glass) which had been heated inadvance in the same manner as in the first embodiment were prepared.Also, glass substrate B ("AN-2" non-alkali glass) which had never beenheated were prepared. First, volume of each substrate was measured atroom temperature (the volume obtained is referred to as V₁). Then theseglass substrates were heated at various temperatures for 12 hours. Afterthe heating process, volume of each substrate was measured again at roomtemperature (the volume obtained is referred to as V₂). Then, shrinkingpercentage of each substrate was calculated by the volume V₁ and thevolume V₂ of each substrate. Relationship between the shrinkingpercentages of the heated glass substrates A and the temperatures isshown by line A in FIG. 1, while that in the case of the glasssubstrates B is shown by line B. As apparent from FIG. 1, the shrinkingpercentages of the glass substrates A heated in advance are 1/5 or lessof those of the glass substrates B. It is also found that the shrinkingpercentage tends to be increased exponentially in accordance with theincrease of the temperature. When manufacturing a thin film transistor,since the shrink of previously heated glass substrates aftercrystallization process is 1/5 or less compared with the shrink of notheated glass substrates after crystallization process, error in maskalignment in the subsequent photolithography process in the case of thepreviously heated glass substrates becomes 1/5 or less compared withthat in the case of the non-heated glass substrates. Therefore, itbecomes possible to manufacture a large-sized thin film transistor byone step.

Next, relationship between shrinking percentages and periods of heatingprocess is examined.

Glass substrates A' ("AN-2" non-alkali glass) which had been heated inadvance in the same manner as in the first embodiment and glasssubstrates B' ("AN-2" non-alkali glass) which had never been heated wereprepared. First, volume of each substrate was measured at roomtemperature (the volume obtained is referred to as V₁). Then these glasssubstrates were heated at 600° C. for various periods of time. After theheating process, volume of each substrate was measured again at roomtemperature (the volume obtained is referred to as V₂). Then, shrinkingpercentage of each substrate was calculated by the volume V₁ and thevolume V₂ of each substrate. Relationship between the shrinkingpercentages of the heated glass substrates A' and the periods of heatingis shown by curve A' in FIG. 2, while that in the case of the glasssubstrates B' is shown by curve B'. As apparent from FIG. 2, the glasssubstrates shrink within the first several hours of the heating process,and the curves A' and B' have a tendency to be saturated with thepassage of the time of heating. In the case of the heating for 96 hours,the shrink of the glass substrate B' is about 2000 ppm, while that ofthe glass substrate A' is only about 500 ppm. It is obvious from FIGS. 1and 2 that, when manufacturing a thin film transistor, the shrink of aglass substrate after crystallization process can be decreased byheating a glass substrate in advance.

FIG. 3 shows relative intensity in Raman spectroscopic analysis forsemiconductor layers. In the figure, curve a indicates that for asilicon semiconductor layer (a) crystallized in accordance with thefirst embodiment. Curve b indicates that for a semiconductor layer (b)which was formed in the same manner as in the first embodiment exceptthat a glass substrate (AN-2 non-alkali glass) which had never beenheated was utilized instead of the previously heated glass substrate.Also, curve c indicates that for a semiconductor layer (c) which wasformed in the same manner as in the first embodiment except that aquartz substrate was utilized instead of the previously heated AN-2non-alkali glass substrate. The ordinate in FIG. 3 shows the relativestrength of crystallinity of semiconductor layers. As apparent from FIG.3, the crystallinity of the silicon semiconductor layer (a) obtained inaccordance with the first embodiment is far stronger than that of thesemiconductor layers (b) and (c). The semiconductor layers (a) and (c)show sharp peaks at the same wavenumber respectively, and the locationof these sharp peaks is peculiar to polycrystal silicon. Accordingly,the semiconductor layer (c) formed on the quartz substrate as well asthe semiconductor layer (a) formed in accordance with the firstembodiment is polycrystal of high crystallinity. In the siliconsemiconductor layer (a), internal stress generated by thecrystallization process is very little by virtue of the previous heatingof the glass substrate. As in the foregoing description, the previousheating of a glass substrate at a temperature not higher than strainpoint of the glass substrate is advantageous: The shrink of a glasssubstrate after crystallization process is very little and internalstress generated in a crystallized semiconductor layer is very little,whereby crystallinity and electrical property are improved.

With respect to the semiconductor layer (b), a sharp peak thereofappears at a location slightly different from that peculiar topolycrystal silicon, as shown in FIG. 3. This is because the property ofthe semiconductor layer (b) was affected by internal stress generatedtherein.

Activation energy for the "AN-2" non-alkali glass is about 0.08 eV,which is equivalent to transition point of the glass (668° C.). Theactivation energy is calculated with the formula indicating the straightline in FIG. 1, R=A exp (-E_(a) /kT) where A is proportional constant,E_(a) is activation energy, and k is Boltzmann's constant.

The glass substrate heating may be carried out under a reduced pressure,instead of an atmospheric pressure.

Referring next to FIGS. 4(A) through 4(E), manufacture of a polycrystalsilicon thin film transistor will be described in accordance with asecond embodiment of the present invention.

A glass substrate ("AN-2" non-alkali glass) 1 was heated at 610° C. for12 hours in an electrical furnace. This heating was carried out in aninactive gas atmosphere, e.g. N₂, under an atmospheric pressure. It maybe done in an inactive gas atmosphere involving an additive of hydrogenunder an atmospheric pressure or a reduced pressure, instead.

On the glass substrate 1, a silicon compound layer 2, e.g. SiO₂ layer,was formed to be 200 nm thick by RF sputtering method. The formation wascarried out under conditions of a pressure of 0.5 Pa, a temperature of100° C., an RF frequency of 13.56 MHz, and an RF output power of 400 W.

Then, an amorphous silicon activation layer 3 was formed to be 100 nmthick on the silicon compound layer by RF sputtering. In this case, theformation was carried out under a pressure of 0.5 Pa at a temperature of150° C. at an RF frequency of RF of 13.56 MHz at an RF output power of400 W.

The amorphous silicon layer 3 was then crystallized by heat at 400° C.to 800° C., typically 500° C. to 700° C., e.g. 600° C., for 96 hours inan inactive gas atmosphere, e.g. N₂, under an atmospheric pressure. Thiscrystallization process may be carried out under a high vacuumcondition.

The crystallized silicon layer 3 was partially removed so that thepattern shown in FIG. 4(A) was obtained.

Subsequently, an n⁺ -type amorphous silicon layer 4 was formed to be 50nm thick by PCVD under a pressure of 6.65 Pa at a temperature of 350° C.at an RF frequency of 13.56 MHz at an RF output power of 400 W at theratio of PH₃ (5%):SiH₄ :H₂ =0.2 SCCM:0.3 SCCM:50 SCCM. The silicon layer4 was then partially removed so that a gate region was formed as shownin FIG. 4(B).

A gate oxide film (SiO₂) 5 was formed to be 100 nm thick by sputteringas shown in FIG. 4(C), under conditions of a pressure of 0.5 Pa, atemperature of 100° C., an RF frequency of 13.56 MHz, and an RF outputpower of 400 W. Then the gate oxide film 5 was partially removed tothereby form contact holes as shown in FIG. 4(D).

Finally, an aluminum layer of 300 nm thickness was formed by vacuumdeposition and then patterned into electrodes 6, whereby a polycrystalsilicon thin film transistor (a) as shown in FIG. 4(E) was completed. InFIG. 4(E), S indicates a source electrode, G a gate electrode, and D adrain electrode.

For a comparison thereto, another polycrystal silicon thin filmtransistor (b) was manufactured in the same manner as in the secondembodiment, except that an "AN-2" non-alkali glass substrate which hadnot been heated was utilized instead of the previously heated "AN-2"non-alkali glass substrate. Also, a polycrystal silicon thin filmtransistor (c) was manufactured in the same manner as in the secondembodiment except that a quartz substrate was utilized instead of thepreviously heated "AN-2" non-alkali glass substrate. I_(D) (draincurrent)-V_(G) (gate voltage) characteristics of thin film transistors(a), (b), and (c) are indicated by curves a, b, and c in FIG. 5. It isapparent from FIG. 5 that the I_(D) -V_(G) characteristic of the thinfilm transistor (a) is improved so much in comparison to that of thethin film transistor (b), and also the electrical property of thetransistor (a) is close to that of the thin film transistor (c).

The relationship between gate voltage and field effect mobility of thethin film transistors (a), (b), and (c) is illustrated in FIG. 6. InFIG. 7 are shown field effect mobilities, where alphabet a indicates thethin film transistor manufactured in accordance with the secondembodiment, alphabet b indicates a thin film transistor manufactured inthe same manner as that of the above thin film transistor (b), andalphabet c indicates a thin film transistor manufactured in the samemanner as that of the above thin film transistor (c). It is found inFIGS. 6 and 7 that the field effect mobility of the thin film transistora is larger than that of the thin film transistor b and is almost thesame as that of the thin film transistor c.

In accordance with a third embodiment of the present invention,formation of a semiconductor layer on a substrate will be describedhereinafter.

An "AN-2" non-alkali glass whose strain point is 616° C., was utilizedas a substrate. This glass substrate was heated at 610° C. for 12 hoursin an electrical furnace. This heating process was carried out in aninactive gas atmosphere, e.g. N₂, involving hydrogen at 50% under anatmospheric pressure. Then a silicon compound layer, e.g. SiO₂ layer,was formed to be 200 nm thick by magnetron RF sputtering, andsubsequently an amorphous silicon layer was formed thereon to be 100 nmthick by means of a magnetron RF sputtering apparatus in an atmosphereof a hydrogen partial pressure of 0.75 mTorr and an argon partialpressure of 3.00 mTorr at an RF power of 400 W, utilizing a target madeof silicon. Then the amorphous silicon layer was crystallized by heat at600° C. for 96 hours.

Shrinking percentages of glass substrates D which had been heated inadvance in the same manner as in the third embodiment were measured.Also, those of glass substrates E which had not been heated were alsomeasured. Relationship between shrinking percentages of the glasssubstrates D and E and temperatures is shown by lines D and E in FIG. 8respectively. Note the shrinking percentage of each substrate in FIG. 8was calculated in the same manner as in FIG. 1. As apparent, theshrinking percentages of the heated glass substrates D were far lowerthan those of the glass substrates E not heated.

Then, relationship between shrinking percentages and periods of heatingis examined. Glass substrates D' ("AN-2" non-alkali glass) previouslyheated in the same manner as in the third embodiment and glasssubstrates E' ("AN-2" non-alkali glass) which had never been heated wereheated at 600° C. The relationship between the shrinking percentages ofthe substrates D' and E' and the periods of heating is illustrated withcurves D' and E' in FIG. 9. Note the shrinking percentage of eachsubstrate in FIG. 9 was calculated in the same manner as in FIG. 2. Theresult is that, in the case of heating glass substrates for 96 hours,the shrink of the glass substrate E' was about 2000 ppm, while that ofthe glass substrate D' was only about 500 ppm.

FIG. 10 shows relative intensity in Raman spectroscopic analysis forsemiconductor layers. In the figure, curve d indicates that for asilicon semiconductor layer (d) crystallized in accordance with thethird embodiment. Also, curve e indicates that for a siliconsemiconductor layer (e) which was formed in the same manner as in thethird embodiment except that a not heated "AN-2" non-alkali glasssubstrate was utilized instead of the previously heated "AN-2"non-alkali glass substrate and that an amorphous silicon layer wasformed by plasma CVD instead of sputtering method. Further, curve findicates that for a silicon semiconductor layer (f) which was formed inthe same manner as in the third embodiment except that a quartzsubstrate was utilized instead of the previously heated "AN-2"non-alkali glass substrate and that an amorphous silicon layer wasformed by plasma CVD instead of sputtering method. The semiconductorlayer (f) was polycrystal. The ordinate in FIG. 10 shows relativestrength of crystallinity of semiconductor layers. It is found from FIG.10 that the crystallinity of the silicon semiconductor layer (d) inaccordance with the third embodiment is remarkably high compared withthat of the semiconductor layers (e) and (f). The semiconductor layer(d) shows a sharp peak at the same wavenumber as that of thesemiconductor layer (f). This means that the silicon semiconductor layer(d) in accordance with the third embodiment as well as the semiconductorlayer (f) is polycrystal of high crystallinity.

The semiconductor layer (e) showed a sharp peak at a location slightlydifferent from that of polycrystal silicon, as shown in FIG. 10.

FIG. 11 shows relative intensity in Raman spectroscopic analysis forsemiconductor layers. In the figure, curve D indicates that for asemiconductor layer (d) formed in accordance with the third embodiment.Also, curve F indicates that for a semiconductor layer (F) which wasformed in the same manner as in the third embodiment except thathydrogen was not introduced into a magnetron RF sputtering apparatusduring formation of an amorphous silicon layer and that argon partialpressure was maintained at 3.75 mTorr in the apparatus during theformation of the amorphous silicon layer. Further, curve G indicatesthat for a semiconductor layer (G) which was formed in the same manneras in the third embodiment except that hydrogen partial pressure andargon partial pressure were maintained at 0.15 mTorr and 3.50 mTorrrespectively in a magnetron Rf sputtering apparatus during formation ofan amorphous silicon layer. With respect to the case of F where hydrogenwas not introduced and the case of G where hydrogen partial pressure wasmaintained at 0.15 mTorr, they did not show sharp peaks at a wavenumberof 520 cm⁻¹. On the other hand, in the case of the semiconductor layer(d) formed in accordance with the third embodiment, it showed a sharppeak at a wavenumber of 520 cm⁻¹, which means the semiconductor layer(d) is polycrystal. It is found from the above result that introducinghydrogen into a magnetron Rf sputtering apparatus during sputtering ispreferable. This is because, by introducing hydrogen during sputtering,micro structure is prevented from being formed in the semiconductorlayer and thereby crystallization can be carried out with lessactivation energy. In the case that hydrogen was introduced duringsputtering, a semiconductor layer could be crystallized at 800° C. orless.

The glass substrate heating may be carried out under a reduced pressureinstead of an atmospheric pressure.

Referring next to FIGS. 12(A) through 12(E), manufacture of apolycrystal silicon thin film transistor will be described in accordancewith a fourth embodiment of the present invention.

A glass substrate 11 ("AN-2" non-alkali glass) was cleaned by means ofultrasonic wave. The glass substrate 11 was then heated at 610° C. for12 hours. The glass substrate heating was carried out in an inactive gasatmosphere, e.g. N₂, involving hydrogen at 50% under an atmosphericpressure.

Then a silicon compound layer 12, e.g. SiO₂ layer, was formed to be 200nm thick on the glass substrate 11 by magnetron RF sputtering method.The formation was carried out in an argon atmosphere under a pressure of0.5 Pa at a temperature of 100° C. at an RF frequency of 13.56 MHz at anRF output power of 400 W.

On the silicon compound layer, an amorphous silicon activation layer 13was formed to be 100 nm thick by magnetron RF sputtering method. Theformation was carried out in an atmosphere of hydrogen partial pressureof 0.75 Torr and argon partial pressure of 3.00 Torr at a temperature of150° C. at an RF frequency of 13.56 MHz at an RF output power of 400 W.

Then the amorphous silicon layer 13 was crystallized by heat in aninactive gas atmosphere, e.g. N₂, under an atmospheric pressure in anelectrical furnace for 96 hours at a temperature of 400° to 800° C.,typically 500° to 700° C., e.g. 600° C. This crystallization process maybe carried out in a hydrogen or carbon monoxide atmosphere or in aninactive gas atmosphere involving hydrogen or carbon monoxide, in orderto prevent the amorphous silicon layer from reacting with a gas, e.g.oxygen.

The crystallized silicon layer 13 was partially removed so that apattern in FIG. 12(A) was obtained.

Subsequently, an n⁺ -type amorphous silicon layer 14 was formed to be 50nm on the silicon layer 13 by magnetron RF sputtering method. Theformation was carried out in an atmosphere of hydrogen partial pressureof 0.75 Torr, argon partial pressure of 3.00 Torr and PH₃ partialpressure of 0.05 Torr at a temperature of 150° C. at an RF frequency of13.56 MHz at an RF output power of 400 W. Then the silicon layer 14 waspartially removed to obtain a gate region as shown in FIG. 12(B). Then,a gate oxide film (SiO₂) 15 was formed to be 100 nm thick by magnetronRF sputtering under a pressure of 0.5 Pa at a temperature of 100° C. atan RF frequency of 13.56 MHz at an RF output power of 400 W as shown inFIG. 12(C).

The gate oxide film 15 was then partially removed to thereby formcontact holes as shown in FIG. 12(D).

Finally, an aluminum layer of 300 nm thickness was formed by vacuumdeposition and then patterned into electrodes 16, whereby a polycrystalsilicon thin film transistor shown in FIG. 12(E) was completed. In FIG.12(E), S indicates a source electrode, G a gate electrode, and D a drainelectrode.

For a comparison thereto, polycrystal silicon thin film transistor (h)was manufactured in the same manner as in the fourth embodiment exceptthat an amorphous silicon activation layer 13 was formed by plasma CVDinstead of magnetron RF sputtering method. In FIG. 13 is shown I_(D)-V_(G) characteristic of the thin film transistor (h) by curve h. Also,that of a thin film transistor (g) in accordance with the fourthembodiment is shown by curve g. As apparent from FIG. 13, the I_(D)-V_(G) characteristics of the above two thin film transistors are veryclose. Also, relationship between gate voltage V_(G) and field effectmobility μ with respect to the thin film transistor (g) and that withrespect to the thin film transistor (h) are shown by curves g and h inFIG. 14 respectively. As obvious from the figure, field effectmobilities of the two thin film transistors (g) and (h) are very close.From these results, it is recognized that characteristic of the thinfilm transistor (h) in which the amorphous silicon layer 13 is formed byplasma CVD is almost the same as that of the thin film transistor (g) inaccordance with the fourth embodiment.

For a further comparison, a polycrystal silicon thin film transistor (i)was manufactured in the same manner as in the fourth embodiment exceptthat a glass substrate was heated in a nitrogen atmosphere to whichhydrogen was not added. I_(D) -V_(G) characteristic of the thin filmtransistor (i) is shown by curve i in FIG. 15. That of the thin filmtransistor (g) in accordance with the fourth embodiment is shown bycurve g. It is apparent from FIG. 15 that the characteristic of the thinfilm transistor (g) is superior to that of the thin film transistor (i).This is because the hydrogen etched oxygen residing on the glasssubstrate in the thin film transistor (g), and accordingly electricalproperty of the thin film transistor (g) was not degraded. In the fourthembodiment, heating and cleaning of the glass substrate were carried outin one step. For reducing the number of manufacturing steps, it ispreferred to heat a glass substrate in an inactive gas atmosphereinvolving hydrogen, as explained hereinbefore. Carbon monoxide alsofunctions to clean up oxygen on a glass substrate, so that the glasssubstrate heating may be carried out in an inactive gas atmosphereinvolving carbon monoxide.

Referring next to FIGS. 16(A) through 16(E), manufacture of apolycrystal silicon thin film transistor of coplanar type in accordancewith a fifth embodiment of the present invention will be described.

A glass substrate ("AN-2" non-alkali glass) 21 was heated at 610° C. for12 hours in an electrical furnace. This heating was carried out in aninactive gas atmosphere, e.g. N₂, under an atmospheric pressure. Theglass substrate heating may be carried out in a hydrogen or a carbonmonoxide atmosphere or in an inactive gas atmosphere involving hydrogenor carbon monoxide.

A silicon compound layer, e.g. SiO₂ layer, 22 was formed to be 200 nm byRF sputtering under a pressure of 0.5 Pa at a temperature of 100° at anRF frequency of 13.56 MHz at an RF output power of 400 W.

On the silicon compound layer 22, an amorphous silicon activation layer23 of 100 nm thickness was formed by RF sputtering under a pressure of0.5 Pa at a temperature of 150° C. at an RF frequency of 13.56 MHz at anRF output power of 400 W.

The amorphous silicon layer 23 was then crystallized by heat at atemperature of 400° C. to 800° C., typically 500° C. to 700° C., e.g.600° C., for 96 hours in a nitrogen atmosphere involving carbon monoxideat 50%. This crystallization was carried out in an electrical furnaceunder an atmospheric pressure or a reduced pressure. Since carbonmonoxide oxidized oxygen residing on the glass substrate, the amorphoussilicon layer 23 was not affected by oxygen. The crystallization processmay be carried out by irradiating partially the silicon layer 23 withlaser so that the temperature of the silicon layer 23 is 400° C. to 800°C. In this case, at least a portion of the silicon layer 23 irradiatedwith laser is crystallized to be utilized as a channel region.

Then, the crystallized silicon layer 23 was partially removed to form apattern in FIG. 16(A). Reference numeral 23 in FIG. 16 designates achannel region formed of the crystallized silicon layer.

An n⁺ -type amorphous silicon layer 24 was formed to be 50 nm thick byPCVD method under a pressure of 6.65 Pa at a temperature of 350° C. atan RF frequency of 13.56 MHz at an RF output power of 400 W at a ratioof PH₃ (5%): SiH₄ : H₂ =0.2 SCCM: 0.3 SCCM: 50 SCCM. The amorphoussilicon layer 24 was partially removed to form a gate region as shown inFIG. 16(B).

Then, a gate oxide film (SiO₂) 25 of 100 nm thickness was formed bysputtering under a pressure of 0.5 Pa at a temperature of 100° C. at anRF frequency of 13.56 MHz at an RF output power of 400 W as shown inFIG. 16(C). The gate oxide film 25 was then partially removed to formcontact holes as shown in FIG. 16(D).

Finally, an aluminum layer of 300 nm thickness was formed by vacuumdeposition and then patterned into electrodes 26, and a polycrystalsilicon thin film transistor (j) shown in FIG. 16(E) was thus completed.In FIG. 16(E), S is a source electrode, G a gate electrode, and D adrain electrode.

For a comparison thereto, a polycrystal silicon thin film transistor (k)was manufactured in the same manner as in the fifth embodiment exceptthat a not heated glass substrate ("AN-2" non-alkali glass) was utilizedinstead of the previously heated "AN-2" non-alkali glass substrate.Also, a polycrystal silicon thin film transistor (m) was manufactured inthe same manner as in the fifth embodiment except that a quartzsubstrate was utilized instead of the previously heated "AN-2"non-alkali glass substrate. I_(D) -V_(G) characteristics of the thinfilm transistors (j), (k), and (m) are shown by curves j, k, and m inFIG. 17 respectively. It is found from the figure that the I_(D) -V_(G)characteristic of the thin film transistor (j) in accordance with thefifth embodiment is far improved compared with the thin film transistor(k) utilizing a not heated glass substrate. Electrical property of thethin film transistor (j) is close to that of the thin film transistor(m) formed on a quartz substrate.

FIG. 18 shows relationship between gate voltage V_(G) and field effectmobility μ of the thin film transistor (j), (k), and (m). FIG. 19 showsfield effect mobility μ, where alphabet j indicates a thin filmtransistor manufactured in the same manner as that of the thin filmtransistor (j), alphabet k indicates a thin film transistor manufacturedin the same manner as that of the thin film transistor (k), and alphabetm indicates a thin film transistor manufactured in the same manner asthat of the thin film transistor (m). As apparent from FIGS. 18 and 19,the field effect mobilities μ of the thin film transistors (j) inaccordance with the fifth embodiment are higher than those of the thinfilm transistors (k) manufactured on not heated "AN-2" non-alkali glasssubstrates and are almost the same as those of the thin film transistors(m) manufactured on quartz substrates.

For a further comparison, thin film transistors (n) were manufactured inthe same manner as in the fifth embodiment except that the amorphoussilicon layer 23 was crystallized in an atmosphere of 100% nitrogeninstead of the nitrogen atmosphere involving carbon monoxide at 50%. Inthese thin film transistors (n), field effect mobility exceeding 100cm⁻² /V_(s) could not be obtained. To the contrary, with respect to thethin film transistors manufactured in accordance with the fifthembodiment, 10% or higher of all the products had field effect mobilityexceeding 120 cm⁻² /V_(s). In FIG. 20, I_(D) -V_(G) characteristics ofthe thin film transistors (j) and (n) are shown by curves j and n. Asapparent from FIG. 20, the thin film transistor (j) manufactured inaccordance with the fifth embodiment is superior to the thin filmtransistor (n).

The foregoing description of preferred embodiments has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form described, andobviously many modifications and variations are possible in light of theabove teaching. The embodiment was chosen in order to explain mostclearly the principles of the invention and its practical applicationthereby to enable others in the art to utilize most effectively theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated. For example, a non-singlecrystal semiconductor layer may be formed on a glass substrate bychemical vapor deposition method, vacuum deposition method, ion clusterbeam method, MBE (molecular beam epitaxy) method, laser abrasion method,and the like. A polycrystal semiconductor layer of high crystallinitycan be obtained from the non-single crystal semiconductor layer by themethod of the present invention. Also, thin film transistors of staggertype, inverse stagger type, and inverse coplanar type may bemanufactured by the method of the present invention. A glass substratemay be heated in a photo CVD apparatus equipped with heating means,instead of an electrical furnace. In this case, hydrogen is introducedand activated in the photo CVD apparatus during the heating, to therebyenhance the cleaning of a substrate surface.

Further, a silicon nitride layer, a silicon carbide layer, a siliconoxide layer, a silicon oxinitride layer, or a multilayer comprising someof the above layers may be provided on a glass substrate as a blockinglayer, instead of the blocking layer used in embodiments of the presentinvention. By the provision of such a blocking layer, it can be avoidedfor alkali ions residing in a glass substrate to enter a device to beformed on the substrate.

In the foregoing embodiments, a blocking layer is formed on a heatedsubstrate. However, a semiconductor device of the present invention maybe manufactured by forming a blocking layer on a glass substratefollowed by heating the glass substrate provided with the blockinglayer. Also, "LE-30" comprising SiO₂ (60%), Al₂ O₃ (15%), B₂ O₃ (6%),and R₂ O (2%) manufactured by HOYA Corporation, "TRC-5" comprising SiO₂,A1₂ O₃, and ZnO manufactured by Ohara Inc., and "N-O" manufactured byNippon Electric Glass Co., Ltd. may be used instead of "AN-2" non-alkaliglass.

What is claimed is:
 1. In a method for manufacturing a semiconductor device comprising the steps of forming a non-single crystal semiconductor layer on a glass substrate and crystallizing said non-single crystal semiconductor layer, the improvement comprising:heating said glass substrate at a temperature not higher than strain point of said glass substrate before forming said non-single crystal semiconductor layer in an atmosphere comprising a gas selected from the group consisting of hydrogen gas and carbon monoxide gas;.
 2. The method of claim 1 wherein said atmosphere further includes a nitrogen gas.
 3. The method of claim 1 wherein said crystallizing step is carried out in an atmosphere comprising at least one of an inactive gas, nitrogen, hydrogen, and carbon monoxide.
 4. In a method for manufacturing a semiconductor device comprising the steps of forming a non-single crystalline semiconductor layer on a glass substrate and crystallizing said non-single crystalline semiconductor layer at a temperature from 400° C. to 800° C., the improvement comprising:heating said glass substrate before forming said non-single crystal semiconductor layer in an atmosphere comprising a gas selected from the group consisting of hydrogen gas or carbon monoxide gas
 5. The method of claim 4 wherein said atmosphere further includes a nitrogen gas.
 6. The method of claim 4 wherein said crystallizing step is carried out in an atmosphere comprising at least one of an inactive gas, nitrogen, and carbon monoxide.
 7. The method of claim 4 wherein said inactive gas comprises argon.
 8. The method of claims 1 or 4 wherein a silicon compound layer is formed on said glass substrate either before or after said preheating the glass substrate but before forming said non-single crystal semiconductor layer.
 9. The method of claim 8 wherein said silicon compound layer comprises a compound selected from the group consisting of silicon oxide silicon nitride, silicon carbide, and silicon oxynitride.
 10. In a method for manufacturing a semiconductor device on a glass substrate comprising at least a non-single crystal semiconductor layer, the improvement comprising preheating said glass substrate in an atmosphere comprising at least hydrogen or carbon monoxide before forming said non-single crystal semiconductor layer in order to minimize the thermal contraction of said substrate during the formation of said semiconductor layer.
 11. The method of claim 10 wherein said non-single crystal semiconductor is formed by depositing a non-single crystal semiconductor layer by a vapor deposition method and crystallizing said layer by heating. 